1. Field of the Invention
The subject disclosure relates to implantable medical devices, and more particularly, to implantable cardiac leads that include conductors and contacts made from diamagnetic materials to reduce electromagnetic interference and induction heating.
2. Description of Related Art
An electromagnetic interference environment in very close proximity to the human body may create difficulty for implantable medical devices to perform well without compromising the safety and performance of the electromagnetic interference environment.
There is a wide variety of magnetic interference that can be in close proximity to the body (in the pocket) with the use of portable transmitting and receiving electronics, (Cell Phone, Tablet, Laptop) and in some cases multiple combined emissions and their harmonics. These, and other emissions, e.g. through WIFI, metal detectors, and the like, can influence the millivolt level operation signals of the implantable medical devices that can be life critical. For example, if the induced electromagnetic radiation induces a signal out of phase with the normal heart signals, this can cause the signal generator to not operate properly. The different frequency spectrum of these signals makes the design of immune to electrical magnetic interference implantable devices a complex endeavor.
The greatest electromagnetic interference is currently during a Magnetic Resonance Imaging (MRI) session or a Magnetic Resonance Tomography (MRT) imaging session. Current approaches to diminish the electromagnetic induction heating and alteration of the low voltage normal operation signals has been to design ICR (Induction Capacitance Resistance) self-resonant notch filter characteristics by the use of inductance, multi turn coiling of the conductors along with the tuning of the insulation characteristics (capacitance) so that the implanted electrical conductors have a high impedance at a particular frequency.
Series connection of multiple tuned induction capacitive aspects are also used to self-resonate at the two main MRI frequencies of 1.5 Tesla 64 MHz and 3.0 Tesla 128 MHz. This is described in U.S. Pat. Nos. 9,295,828 and 9,492,651. Another method is the use of braid over the length of the conductors where the induction and capacitance of the braid is also carefully tuned to have high impedance at the particular resonance frequency, as described in U.S. Pat. No. 9,463,317, and thereby shield the inner conductors from the electromagnetic induction.
Another method is to alter the surface of the conductors themselves with nanometer and micron size particles of different conductive metals disrupting the flow of the electromagnetic induction into the conductor by creating micro islands of swirling magnetic fields on the surface that do not add to the conductor itself. This is described in U.S. Patent Publication No. 2014/0050861 A1.
These methods are capable of meeting acceptable safety margins. However, it is desired to achieve improved integrity and reliability of the low voltage signals that are in an implanted heart lead, circuitry, defibrillation conductors, circuitry, and many other neuro-stimulation electrical conductors, electrodes, and circuitry. Conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for devices that reduce the electromagnetic induction and interference of implantable electrical devices, conductors and electrodes. This disclosure provides a solution for these needs.